"Greek and Roman demigods from the Prophecy of Seven must work together to seal the Doors of Death--and help Percy and Annabeth escape the Underworld in the process"--

"After exposing the sinister underground society of students known as the Knights of Charlemagne, Will West stays at the Center over the summer to explore his newly developing physical and mental abilities. Meanwhile, his roommates investigate the Knights' shadowy purpose and discover unsettling information about their own backgrounds"--